In many applications, a PCBA is encapsulated to protect attached components, interconnects between components and between components and the PCB, and the PCB itself from environmental conditions, such as humidity. The PCBA can be encapsulated using a coating material that is either sprayed or brushed onto the PCBA, which forms a conformal film. First the surface is cleaned, then the conformal film is applied. A disadvantage of a conformal film encapsulation is that mechanical resistance, such as resistance to abrasion, is lacking. For example, if the conformal film is scratched, there is a high likelihood that the conformal film will be peeled off and the underlying PCBA surface/components penetrated. As such, the conformal film is effective for humidity resistance, but not mechanical resistance. However, even for humidity resistance, conformal film provides limitations. For example, application of the coating material is not always uniform or complete, and therefore the conformal film coverage may not be uniform and there may be coverage incompleteness in some areas that require re-application of the coating material.
Thermoforming is a manufacturing process where a plastic sheet is heated to a sufficient temperature that permits the heated plastic sheet to be stretched into or onto a mold and cooled to a finished shape. Vacuum forming is a simplified version of thermoforming, where a plastic sheet is heated to a forming temperature, stretched onto a single-surface mold, and forced against the mold by a vacuum. Relatively deep contours can be formed if the plastic sheet is stretched prior to bringing it into contact with the mold surface and applying vacuum. Vacuum forming is a process currently used to form variously shaped objects, such as disposable cups or substrates in In-Mold Electronics (IME) having 2D or 2.5D shapes. In IME, a thermoformable plastic sheet is used as a base substrate. Stretchable conductive ink is screen printed onto the thermoformable plastic sheet to form conductive traces, or interconnects, prior to the thermoforming process, then the thermoformable plastic sheet is thermoformed. Components are then added to the thermoformed substrate. Lastly, the thermoformed substrate with attached components is placed in a mold, and an overmold layer is applied over the components and thermoformed substrate using an injection molding process.
At present, overmolding a PCBA by placing the PCBA in a mold and performing injecting molding can be performed, but there are significant risks for the PCBA. Risks include damage to the components due to the heat and pressure, components disconnecting from the PCB due to the plastic material flow, PCBA deformation, and the like.